But it is the answer to the wrong question: the question is not what "chrome" is a derivation of, but why slides are called chromes.
And that is not because "chroma" is greek for colour.

Here'e how I see it. The first REAL color film was Kodachrome. They just happened to call it 'chrome' because it is a color film. But when Kodak later came out with color negative film, they could not call it Kodachrome since 'chrome' was already taken by the famous positive film. So they called it Kodacolor. Thus started the convention of calling slide films 'chrome', and using the 'color' suffix for negative films. Other manufacturers followed suit.